This invention relates to switch assemblies for dynamoelectric machines and in particular to a switch assembly which is adapted to protect the start circuit electrical contact of that the dynamoelectric machine from malfunction because of the presence of foreign matter. While the invention is described with particular emphasis to its use in conjunction with switch contacts, those skilled in the art will recognize the greater adaptability and inventive concepts disclosed hereinafter.
There are certain applications for dynamoelectric machines that place those machines in environments having a high ratio of contaminants in the air to which the dynamoelectric machine is exposed. Two particular applications which easily come to mind are table saw or radial arm saw applications which employ motors to drive the saws, and swimming pool pumps and filter systems which employ motors as the drive source. Conventional wisdom dictates that these applications require the use of "totally enclosed motors." Those skilled in the art will recognize that the term "totally enclosed motor" refers to a motor construction in which the parts of the dynamoelectric machine, i.e., the stator, rotor and switch structure, along with the motor bearings, are protected from the environment in which they operate by specially designed closures or shells, end shields and bearings. Because the stator and rotor assembly of the motor are enclosed, these parts must be designed to operate at reduced temperatures. Generally, this requires longer motor core stack heights and additional winding material. While totally enclosed motors work well for their intended purposes, they are relatively high in cost, as compared to what is known in the art as open motors, especially if an open motor can be substituted directly in a closed motor application. Open motors, while having the same basic components as closed motors, i.e., a stator assembly, a rotor assembly, shell, end shield and bearings to support the shaft, use the environment of the dynamoelectric machine itself for cooling purposes, and consequently, the bearings, the core stack heights, and winding material employed in the stator and rotor assembly may be altered or reduced in one design as compared to the other. Obviously, this gives a lower cost motor for a particular application.
Because of their lower cost, open motors preferably are used where possible. In the past, open motors have been substituted for enclosed motors in table saws and the like. However, the substitution of an open motor in a table saw environment, i.e., where there is a high concentration of sawdust and microscopic particles in the air, has been plagued with motor failures. Motor failures occur because the electrical switch used in association with the open motor often fails. Commonly, the motors employed in these kinds of applications are either split phase or capacitor start, induction run motors. Those skilled in the art will recognize that such motors conventionally employ a centrifugal actuator to control the operation of the starting circuit of the motor. That is to say, at low speeds the actuator closes the switch so that an auxiliary or start winding is connected to a source of electrical energy, while the actuator disconnects the start winding as the motor reaches operating speed. It is the switch structure heretofore employed in making and breaking the electrical contact for the start winding that often malfunctions in the applications described above.
Motors used in conjunction with the pumps for swimming pool filter systems also have exhibited similar failure problems. Switch failure in this kind of application, while not attributable to sawdust in the air, is attributable to the fact that, for whatever reason, flying insects and other bugs seem attracted, or at least find their way into the dynamoelectric machine and often foul the operation of the switch assembly.
A number of attempts have been made in the prior art to alleviate switch failure problems. In particular, attempts have been made to enclose the starting switch contacts in order to protect them from their environment. While this has reduced the failure rate of open motors used in the above applications, it has not solved the problem to a suitable degree. I have found that open motors can be employed in many environmentally contaminated applications when the switch contact is protected by a structure which includes a very soft, pliable washer that has an interference fit in association with the switch terminal on which it is mounted. The entire structure that encloses the switch contact moves in response to forces applied to it by the centrifugal actuator, and the interference fit of the pliable washer effectively seals the electrical contact area. Moreover, the pliable washer must be "set" properly during construction of the dynamoelectric machine so that it is positioned correctly with respect to the switch post on which it is mounted. When this is accomplished, I have found that problems heretofore associated with use of open motors in contaminated environments are surprisingly substantially eliminated.
One of the objects of this invention is to provide an improved switch structure for dynamoelectric machines.
Another object of this invention is to provide a switch structure which prevents the fouling of the electrical contacts when the switch is exposed to an adverse environment.
Another object of this invention is to provide a switch structure for an open motor which includes means for preventing the fouling of at least one electrical contact of the switch.
Another object of this invention is to provide a low cost switch structure for a dynamoelectric machine.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.